1. Field of the Invention
The present invention relates to a method of making a semiconductor device comprising a series of steps for processing a plurality of lots, each including semiconductor substrates to be processed, for every one lot by using the same semiconductor manufacturing apparatus.
2. Description of the Related Art
Reactive ion etching (RIE) apparatus is known to the art as one of semiconductor manufacturing apparatus utilizing plasma. In the RIE apparatus, a negative potential is applied to a wafer and a reactive gas (etching gas) is discharged by using a high frequency power to produce the plasma. The ions contained in the plasma are impinged on the wafer surface in a direction perpendicular to the wafer surface to etch the wafer physically and chemically.
Where a via hole is formed in an insulating film, a gas containing mainly a fluorocarbon is used as the etching gas. To be more specific, in order to prevent a metal wiring layer exposed to the bottom surface of the via hole from being etched, used in general is an etching gas capable of ensuring a selectivity ratio relative to the metal wiring layer, i.e., a gas containing CHF3, C4F8, etc.
If the RIE processing is applied to an insulating film by using the etching gas noted above, the gas within the plasma is decomposed, with the result that a fluorocarbon, carbon, etc. are deposited on an inner wall of a vacuum chamber. In this case, the reaction product, produced during the RIE processing of the insulating film, is also deposited partly to the inner wall of the vacuum chamber.
These fluorocarbon, carbon and reaction product are deposited to the inner wall of the vacuum chamber, thereby forming a deposited film containing fluorocarbon, etc.
The thickness of the deposited film is gradually increased with progress of the processing. When the deposited film grows to reach a certain thickness, the deposited film is peeled from the inner wall of the vacuum chamber to give rise to unwanted generation of particles. In order to prevent such a problem, employed nowadays is the technique that the inner space of the vacuum chamber is allowed to communicate with the air atmosphere before the deposited film grows to reach a certain thickness, thereby carrying out wet cleaning of the inner wall of the vacuum chamber.
The RIE processing of the insulating film includes various patterns, and different gases are selected depending on the requirements of the patterns. For example, a gas different from that used in the RIE processing of the via hole is used in the RIE processing of a wiring groove in a damascene process.
The damascene process is a process that has come to be used in recent years. In the damascene process, a wiring groove is formed in the surface of an insulating film by the RIE process, followed by depositing a metal film for forming a wiring layer on the entire surface in a manner to bury the wiring groove therewith and subsequently removing the undesired metal film outside the wiring groove by CMP (Chemical Mechanical Polishing).
In the case of the damascene process, a high dimensional accuracy is required because the pattern of the wiring layer is determined by the pattern of the wiring groove. Therefore, since the RIE processing of the wiring groove differs from the RIE processing of the via hole, a gas is selected which has the reduced fluorocarbon and carbon when the gas is decomposed.
If a different gas is selected, formed naturally on the inner wall of the vacuum chamber is a deposited film having a different composition. Where RIE processes using different gases are performed within the same vacuum chamber to form a stacked structure of deposited films greatly differing from each other in composition, the deposited films are peeled off for a shorter time at the stage that the deposited films have smaller thicknesses because of, for example, the difference in the thermal expansion coefficient among the deposited films to give rise to the particle generation problem. What should be noted is that the growth of the deposited film to reach a certain thickness is not the sole cause of the peeling of the deposited film.
In order to avoid the problem of this type, the target process performed is limited nowadays in respect of each of a plurality of RIE apparatuses used in view of the composition of the gas used and quality of the deposited film.
Further, where the gases used in different process steps widely differ from each other in composition, an additional problem is generated that the gas released from the deposited film formed in the previous process step affects the succeeding process. Therefore, it is necessary to prepare a large number of RIE apparatus greater than the number of target process steps that are actually performed.
In order to overcome these various problems, it is necessary to remove the deposited film formed immediately before on the inner wall of the vacuum chamber with the plasma (plasma cleaning) when the processing is applied to the subsequent substrate lot Aj (j=i+1) by using the same RIE apparatus after completion of the processing applied to a certain substrate lot Ai (i=1 to 19), as shown in FIG. 3.
However, such a measure shown in FIG. 3 is not practical because a very long time is required if the plasma cleaning is performed every time the processing is applied to the subsequent substrate lots.
As described above, in order to overcome the various problems relating to the peeling of the deposited film, it is necessary to remove the deposited film formed immediately before on the inner wall of the vacuum chamber with the plasma when the subsequent processing is carried out after completion of the same processing. However, the measure is not practical because a very long time is required for removing the deposited film every time the subsequently processing is performed.